A paste containing silver fine particles is used for forming conductive circuits on circuit boards constituting a semiconductor device, electrodes for capacitors, etc., by forming a silver film having electrical conductivity by sintering silver fine particles with heating. In recent years, it has also been used for forming bonded portion in semiconductor devices such as bumps and the die attach materials, etc.
However, when the paste is used for forming a bonding portion such as a semiconductor device, etc., there is a problem that sintering of the silver fine particles in the paste causes volume shrinkage of the paste so that the thickness of the bonded portion between the semiconductor element and the substrate is reduced, so that sufficient bonding strength cannot be obtained. In addition, when the bonded portion are formed by using a paste containing silver fine particles, a thickness of the adhered portion is controlled by subjecting to the pressurizing treatment in addition to the heat treatment. However, in recent years, the size of the semiconductor element becomes small, and accompanied by the reduction of the size of the semiconductor element, it becomes difficult to control the thickness by applying a load to the semiconductor element.
Further, the modulus of elasticity of the bonded portion becomes large by sintering of the silver fine particles in the paste, in other words, the bonded portion become hard so that the bonded portion cannot follow the change in temperature due to repeated use of the electronic parts using the semiconductor element, whereby crack of the semiconductor element, crack at the bonded portion and peeling of the bonding surface, etc., are generated in some cases.
In order to relax the shrinkage stress generated by the volume shrinkage due to sintering of the metal particles in the paste at the bonded portion, it has been proposed a conductive bonding material comprising metal fine particles and metal coated-resin particles in which a metal which is capable of sintering with the metal fine particles is coated onto the surface of the resin particles having a larger particle size than those of the metal fine particles as an aggregate (Patent document 1).
In addition, in order to suppress lowering in connection reliability due to the volume shrinkage of the connection conductor, it has been proposed a filling material for electrical conduction comprising a mixture of a metal filler, a paraffinic hydrocarbon which melts at a temperature lower than the sintering temperature of the metal filler and is a solid state at room temperature, and a resin comprising a turpentine oil or a fatty acid which has a low melting point and is a solid at room temperature (Patent document 2).